Patients with osteoarthritis undergoing total hip or knee arthroplasty were included in a prospective observational study where transfusions and blood loss were registered and related to perioperative characteristics.
Patients and settings
A total of 193 consecutive patients (mean age 67 ± 11 years, 49% women), with the diagnosis osteoarthritis undergoing unilateral primary hip (n = 114) or knee (n = 79) arthroplasty at two centers (Sahlgrenska University Hospital and Kungälv Hospital), were included in the study between October 2009 and January 2011. Exclusion criteria were known liver disease or coagulation disorder.
Ethics, consent, and permissions
The Regional Ethical Review Board in Gothenburg approved the study (date of approval 11 September 2009, reference number 072–08). All patients gave informed written consent before inclusion in the study.
Spinal anesthesia was used in 160 (83%) of the patients (95 hip, 65 knee) and general anesthesia in the remaining patients. Dabigatran was used as thrombosis prophylaxis in 179 patients (104 hip, 75 knee) while 14 patients received low molecular weight heparin (LMWH) (15 hip, 4 knee). The first dose of dabigatran was administered 1–4 h after surgery while the first dose of LMWH was administered in the evening before surgery. All patients received tranexamic acid (Cyklokapron®; Pfizer, Sollentuna, Sweden), 10 mg/kg body weight; for hip patients, one dose after start of anesthesia and one dose 3 h later; for knee patients, one dose 10–15 min before release of the tourniquet and one dose 3 h later, according to the local routine.
All patients in the knee group received cemented prostheses and they were operated with a tourniquet. In the hip group, 55 patients received cemented prostheses, 25 received uncemented prostheses, 9 received hybrid arthroplasties (uncemented acetabular component and cemented femoral component), and 10 received reverse hybrid arthroplasty (cemented acetabular component and uncemented femoral component). None of the knee or hip patients had wound drainage postoperatively.
The following baseline variables were recorded: age; gender; BMI; medication prior to surgery, including the use of acetylsalicylic acid (ASA), nonsteroidal anti-inflammatory drugs (NSAIDs), or selective serotonin receptor inhibitors (SSRIs); type of surgery; and thrombosis prophylaxis. Patients on ASA or NSAIDs were urged to discontinue these medications 3 days before surgery. Medication with potent platelet inhibitors, such as clopidogrel, were stopped at least 1 week before surgery. Blood samples from a peripheral vein for hemoglobin (Hb), platelet count, activated partial thromboplastin time (aPTT), and prothrombin time (PT) analyses were obtained <24 h before surgery. Hemoglobin level was also measured 24–48 h postoperatively in order to calculate blood loss.
The following perioperative variables were recorded: duration of operation, bleeding during surgery (intraoperatively), transfusion requirements intraoperatively, and postoperatively until discharge or until reoperation and autologous transfusion of wound blood after cell saver processing. Intraoperative bleeding was calculated from blood retrieved from wound suction plus the estimated amount of blood in the swabs.
Whole blood samples for determination of Hb and platelet count analyses were collected in K2 EDTA plastic tubes (1.8 g/L EDTA; BD Vacutainer, Plymouth, UK). For PT and APTT analyses, blood samples were collected in citrated plastic tubes (2.7 mL 0.129 mmol/L sodium citrate; BD Vacutainer, Plymouth, UK). Hb, platelet count, aPTT, and PT were analyzed with clinical standard methods at the accredited local hospital laboratories. PT is reported as the international normalized ratio (INR); reference value: <1.2. The reference value for APTT is 30–42 s.
Definitions and formulae
Estimated blood loss (EBL) was calculated based on the drop in Hb between the preoperative measurements and the measurements 24–48 h postoperatively according to a formula developed by Brecher . Only intraoperative transfusions are included in the calculation since none of the patients received postoperative transfusion in the interval between end of surgery and before the blood sample taken 24–48 h postoperatively for Hb determination. The formula used was as follows: EBL = ((“estimated blood volume (EBV)” × “hematocrit preoperatively” − EBV × “hematocrit postoperatively”) + (“intraoperative RBC transfusion” × 200 + “intraoperative Cellsaver transfusion” × 0.55)) / 0.35 .
For EBV, the formula is as follows: EBV = (0.0235 × height in cm^0.42246 × weight in kg^0.51456) × k, where k = 2,430 for women and 2,530 for men. Patients in the upper 75th percentile of EBL/kg in the hip and knee group, respectively, were defined as excessive bleeders while all other patients were considered to be non-excessive bleeders.
The study population was also divided into a transfusion group with those patients who received allogeneic RBC transfusions until discharge from hospital and a no-transfusion group with the patients who did not receive any allogeneic RBC transfusion. No pre-specified transfusion criteria were used during the study period, i.e., transfusions were prescribed at the discretion of the attending physician.
Continuous variables were compared with Student t-test or Mann-Whitney U test, and categorical variables were compared with Chi-square test. In the statistical analysis, PT was considered a continuous variable. Statistical significance was defined as a p value of <0.05. Statistical models for identification of predictors of blood loss and transfusion were made with logistic regression analysis. For multiple regression analysis, stepwise logistic regression analysis was used. The following variables were included in the analysis: age; gender; BMI; use of NSAIDs, ASA, or SSRI before surgery; type of anesthesia; operation time; and preoperative Hb, platelet count, PT, and aPTT. For analyses of RBC transfusions, weight was also included. For statistical calculations, IBM SPSS 20.0 software was used.